In an electrical substation, the fundamental aspects that have to be taken into account for implementation correspond to: the electrical configuration, the electrical insulation technology to be used, and the physical layout of its equipment.
With regard to the electrical configuration of a substation, this is determined by the layout and interconnection of the different elements that form the equipment in general, such as the circuit breakers, disconnectors, transformers for measuring intensity and voltage, electric bars, etc.
Different types of configurations are known and those denominated “one and a half breaker”, “double bar” and “classic ring” can be quoted as the most important or those habitually employed. A cutoff element (circuit breaker) and various ones for handling (disconnector) are required in each of these for each input and output position of the substation (line, power transformer, reactance, condenser bench, etc) each substation having an indeterminate number of outputs and inputs.
Of the different types of configuration referred to, that denominated “one and a half breaker” is the most appropriate for critical substations in high voltage, for making the maintenance and operating needs of the system compatible to a great extent (safety, reliability, enlargement, etc) within the cost level acceptable.
The “double bar” configuration is more economic than the “one and a half breaker” one but offers fewer services with regard to availability and flexibility in operating.
The “single bar” configuration is more economical but has the inconvenience that behaviour with regard to availability and flexibility is unacceptable for the most critical voltage levels.
The “classic ring” configuration permits acceptable possibilities for operating at a relatively economic cost, but has the inconvenience that the configuration in itself is very rigid with regard to enlargement.
With regard to the electrical insulation technology conventionally used, this may be exposed to the elements or conventional, that is to say, using the dielectric characteristics of the air, or sulphur hexafluoride (SF6), also denominated armoured.
In the first case, important dimensions are required to guarantee the insulation necessary between phases, the insulation being subject to atmospheric agents that can, in an unexpected manner, cause deterioration, premature ageing and faults in the equipment. For its part, the switchgear, that is to say, the group of elements that constitute the substation, can be independent and permit open solutions, or what is the same, each element or device can be from a different manufacturer.
With regard to the second type of electrical insulation, that is to say, that which uses armoured technology, as the elements are encapsulated in a more insulated environment than air, this permits much more reduced dimensions, with less environmental impact and considerable lower fault indices. On the contrary, they are habitually closed solutions, that is to say, a sole manufacturer exists per installation, forcing dependence on same during the useful life of the substation, in such a way that the repercussions of the faults tend to be serious since they suppose greater unavailability of the installation and affect a greater number of elements, without forgetting that the initial cost is substantially greater than that required for electrical insulation exposed to the elements or conventional.
With regard to the physical layout, or third aspect that has to be taken into account in an electrical substation, different solutions are conventionally offered depending on the other aspects quoted (configuration and insulation technology), together with the operating needs required, an initial definition being necessary that is difficult to modify in the future. In general, three-phase layouts tend to be defined on three heights.
For a balanced distribution of load, that is to say, to avoid power flows of great magnitude over the element (for example, a circuit breaker that joins one side and the other of the substation), and to limit accidents, repercussions on other elements outside the problem, it tends to be recommendable to confront generation inputs with consumption outputs and alternate these confrontations in a reciprocal manner. That is to say, if there are two generation/consumption lines face to face, an attempt must be made for the adjacent confrontation to be consumption/generation, which requires large dimensions and crossings on the majority of the occasions, to make the lines arrive on the correct side, with considerable economic and environmental cost.